The present invention relates to microtubing and more particularly to microtubing of variable stiffness over the length of the tubing. The microtubes of the present invention are typically manufactured at least partially of cured resin and are of outer diameter less than 0.225 inches (5.715 mm). The microtubes of this invention may usefully be employed in a variety of applications such as medical catheters for various diagnostic and therapeutic purposes.
Fine gauge microtubing has been made for many years by coating a surface treated copper mandrel wire with one or more suitable curable resins and subsequently removing the mandrel wire after the resin coating has been cured. In this regard, attention is directed to U.S. Pat. No. 4,051,284 issued to Ohkubo, et al. on Sep. 27, 1977, and entitled xe2x80x9cMethod for Producing Heat Resistant Synthetic Resin Tubes,xe2x80x9d the entire content of this prior U.S. Patent being expressly incorporated by reference.
In medical applications, such as guide catheters, it is usually desirable that the hollow tube or microtube portion of the catheter have characteristics which vary over the length of the tube. Characteristics that are particularly desirable along various portions of catheter tubes include torque transmission or pushability, stiffness or flexibility, burst strength, and kink resistance. It is also necessary that the components of microtubes used in catheters be bio-compatible so as not to induce thrombosis or other trauma when used.
The present invention is a novel multi-layer resin cured microtube. Resin cured layers of the microtube are generally comprised of polyimides, fluoropolymers, and urethanes, and such layers may be interspersed with one or more layers of coiled or braided metal wire or ribbon, or fibers, such as particularly glass, plastic or aramid fibers. The novel microtubes are manufactured according to a continuous process and selected layers or portions of layers may be removed by grinding or etching portions of the tubes. In addition, the number of braid picks per inch and diameter of the tubing may vary along portions of the tube. By varying the materials comprising the layers of the microtubes, and in some instances the thickness of those layers, together with the braid pick count and microtubing diameter and shape, as well as selectively removing portions of resin or braid layers, it is possible to achieve variations in tubing stiffness on the order of over 100 to 1. In other words, for a given length of microtube, the proximal end may be over 100 times stiffer than the distal end. To obtain such wide variations in stiffness previously it has been necessary to fabricate tubing from separate tubing components.
In preferred embodiments of the present invention, the composite microtubes have wall thicknesses of about 0.0025 inches (0.0635 mm) to about 0.01 inches (0.254 mm), inner diameters of 0.005 inches (0.127 mm) or even less to about 0.2 inches (5.08 mm), and outer diameter of 0.01 inches (0.254 mm) to 0.22 inches (5.588 mm). Braid pick counts per inch may range from as few as 30 to 45 picks/inch up to as many as 280 picks/inch. The inner diameter of the microtubing may also vary so that the widest diameter is as much as twice the size as the narrowest diameter. When the layers, braid pick count, or diameter of the composite microtubing are varied, such variation preferably take place gradually over a length of approximately 1 inch or more to reduce the likelihood of kinking in the microtubing.